Sterling has also risen 2.6 per cent on the euro to above €1.30, with the market taking its cue from polls leaning towards a vote to Remain.

In scenes reminiscent of the queues that formed outside branches of Northern Rock and led to its collapse in 2007, City workers queued impatiently around the block outside forex bureaux on Wednesday afternoon.

Summaya, a 31-year-old employee of a retail bank who declined to give her surname, lined up outside the Foreign Exchange Services shop on Cannon Street. She said she was going to change “several thousand pounds” into US dollars and euros because she was convinced the public mood was shifting in favour of Brexit.

“I’m protecting my money. I will stick it under the mattress until Friday,” she said, adding that Tuesday night’s televised debate had swung opinion among her friends and colleagues in favour of Brexit. “People are changing their views.”

Travelex said online orders on Tuesday were 30 per cent higher than the previous week and there was a 20 per cent increase on people visiting its site in the past two days. “Today we’ve also seen an increase in calls to our call-centre,” said David Swann of Travelex.

The Post Office said Tuesday’s sales of foreign currency were nearly four times higher than the same date last year, while sales in branches were nearly 49 per cent higher.

Currency sales on Tuesday were up 74 per cent year on year, said the Post Office.

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Thomas Cook said: “There’s been a surge in customers buying euros in the last six weeks and euro sales have been consistently strong, building day by day.”

Several economists predict a Leave outcome would trigger a dramatic fall in the pound when markets open on Friday, while a vote to Remain should see the pound rally.

But several analysts said this week’s sharp sterling recovery probably limited the scope of the currency’s rise.

Daniel Priori, an Italian who has been working as a cashier at the International Currency Exchange kiosk at Waterloo station for a year, said he and his two colleagues had dealt with many more customers than usual.

Asked why, he replied: “Because they are scared about tomorrow.” He said the majority of transactions were people changing sterling into euros.

But several of those queueing were exchanging their holiday money. Standing in a queue outside Thomas Exchange on Cannon Street, 44-year-old Chris Nobbs, who works in insurance, said: “I go to Alicante in Spain in a couple of weeks, so I’m just taking my euros out today instead of next week. I do not take more than what I need on holiday, but who knows, maybe this will earn me some extra cups of coffee.”

Martin Wolf

The democratic EU of today owes immeasurably to British politics, values and courage

Sunday, 18 February, 2018

Sporting an “In” sticker on her lapel, Charlie Gill, 23, who works in financial services, said: “I visit my family in Germany a couple of times a year, so I’d rather get money out now, and keep it for when I visit them.”

In the queue outside City Forex, on Leadenhall Street, City worker Ed was planning to change “a few hundred quid” before travelling to Greece on holiday next week.

“I don’t have a strong sense of the [referendum] result, but just want to hedge against the downside. I’ll change half now and half later,” he said.

All parts of the forex market are facing a tumultuous 48 hours. Currency traders have been warned by money transfer operators, including TransferWise, to expect restrictions on transactions on Thursday and Friday due to market swings, while several banks are manning their London forex desks overnight to cope with client demand.

UK’s EU referendum: full coverage and analysis

View the FT’s comprehensive guide to the vote on whether Britain should stay in Europe, with all the latest news, analysis and commentary from both sides of the debate. See more